Method and apparatus for video coding

ABSTRACT

Methods, apparatuses, and a non-transitory computer-readable medium for video encoding/decoding are provided. In a method, a block vector of a current block of a coding tree unit (CTU) that is coded in intra block copy (IBC) mode is determined. The block vector indicates a reference block in a search region for the current block. Reference samples to reconstruct the current block in the IBC mode are contained in a reference sample memory including a plurality of memory regions. The current block is coded based on the reference block. A subset of the plurality of memory regions of the reference sample memory is used as the search region. The block vector of the current block is constrained such that the reference block is contained in (i) one of the subset of the plurality of memory regions or (ii) two adjacent memory regions in the subset of the plurality of memory regions.

INCORPORATION BY REFERENCE

This present application is a continuation of U.S. Ser. No. 16/923,599filed on Jul. 8, 2020, which claims the benefit of priority to U.S.Provisional Application No. 62/873,054, “CONSTRAINTS ON REFERENCE SAMPLELOCATIONS FOR IBC WITH DEDICATED BUFFER” filed on Jul. 11, 2019, andU.S. Provisional Application No. 62/873,576, “CONSTRAINTS ON REFERENCESAMPLE LOCATIONS FOR IBC WITH DEDICATED BUFFER” filed on Jul. 12, 2019,which are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate) of, for example, 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or maybe predicted itself.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (105) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs of aneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described herein is atechnique henceforth referred to as “spatial merge.”

Referring to FIG. 1C, a current block (111) can include samples thathave been found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (112 through 116, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods for video encoding/decoding.In a method, prediction information of a current block of a coding treeunit (CTU) in a coded bitstream is decoded. The prediction informationindicates that the current block is coded in intra block copy (IBC)mode. A reference block is determined for the current block. A number ofmemory regions that contain samples of the reference block is less thana total number of memory regions for the CTU. The current block isreconstructed based on the reference block.

In an embodiment, the entire reference block is contained in one memoryregion of the memory regions for the CTU.

In an embodiment, a size of the one memory region is equal to a sizethreshold based on a size of the CTU being greater than or equal to thesize threshold.

In an embodiment, a size of the one memory region is equal to a size ofthe CTU based on the size of the CTU being less than a size threshold.

In an embodiment, an entire column of the samples of the reference blockis contained in one of the memory regions for the CTU.

In an embodiment, an entire row of the samples of the reference block iscontained in one of the memory regions for the CTU.

In an embodiment, a top row of the samples of the reference block isabove a bottom row of the samples of the reference block along avertical direction.

Aspects of the disclosure provide apparatuses for videoencoding/decoding. An apparatus includes processing circuitry thatdecodes prediction information of a current block of a coding tree unit(CTU) in a coded bitstream. The prediction information indicates thatthe current block is coded in intra block copy (IBC) mode. Theprocessing circuitry determines a reference block for the current block.A number of memory regions that contain samples of the reference blockis less than a total number of memory regions for the CTU. Theprocessing circuitry reconstructs the current block based on thereference block.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video encoding/decoding cause the computer to perform anyone or a combination of the methods for video encoding/decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes;

FIG. 1B is an illustration of exemplary intra prediction directions;

FIG. 1C is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example;

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment;

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment;

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment;

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment;

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment;

FIG. 8 shows an example of an intra block copy (IBC) prediction mode, inaccordance with an embodiment;

FIGS. 9A-9D show examples of allowed reference areas in an updatingprocess of the IBC prediction mode, in accordance with an embodiment;

FIGS. 10A and 10B show examples of samples of a reference block fromdifferent regions of a reference sample memory in accordance with anembodiment;

FIG. 11 shows examples where samples of a reference block areconstrained to be within a certain number of memory regions in areference sample memory in accordance with an embodiment;

FIG. 12 shows a flow chart outlining an exemplary process in accordancewith an embodiment; and

FIG. 13 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS I. Video Encoder and Decoder

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick, and the like.

A streaming system may include a capture subsystem (313) that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values that canbe input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation that the intra prediction unit (452) has generated to theoutput sample information as provided by the scaler/inverse transformunit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector allowed reference area,and so forth. The controller (550) can be configured to have othersuitable functions that pertain to the video encoder (503) optimized fora certain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415) andthe parser (420) may not be fully implemented in the local decoder(533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quad-tree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (603), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

II. Intra Block Copy

Block based compensation based on a different picture may be referred toas motion compensation or inter prediction block compensation. Further,block compensation may be performed from a previously reconstructed areawithin a same picture. Such block compensation may be referred to asintra picture block compensation, current picture referencing (CPR), orintra block copy (IBC).

Aspects of the disclosure provide techniques for block basedcompensation within a same picture (e.g., an IBC prediction mode).

According to aspects of the disclosure, in the IBC prediction mode, adisplacement vector that indicates an offset between a current block anda reference block within the same picture is referred to as a blockvector (BV). The reference block is reconstructed prior to the currentblock. In addition, a reference area that is at a tile/slice boundary orwave-front ladder shape boundary may be excluded from being used as anavailable reference block, for example for parallel processing. Due tothese constraints, a block vector is different from a motion vector thatcan have any value (positive or negative, at either the x or ydirection) in the inter prediction mode for example.

The coding of a block vector in the IBC prediction mode can be eitherexplicit or implicit. In the explicit mode, a block vector differencebetween a block vector and a predictor of the block vector is signaled.Coding of a block vector in the explicit mode of the IBC prediction modemay be similar to, for example, coding of a motion vector in an advancedmotion vector prediction (AMVP) mode of the inter prediction mode. Inthe implicit mode, a block vector is recovered from a predictor of theblock vector without using a block vector difference, for examplesimilar to motion vector prediction in merge mode of the interprediction mode. In addition, the resolution of a block vector may berestricted to integer positions in one embodiment but may be allowed topoint to fractional positions in other embodiments.

The use of the IBC prediction mode at the block level can be signaledusing, for example, a block level flag (referred to as an IBC flag) or areference index. When using the IBC flag, the current block may not becoded in implicit mode. When using the reference index, the currentdecoded picture can be treated as a reference picture. For example, thecurrent picture can be put in a last position of a reference picturelist. This reference picture may also be managed together with othertemporal reference pictures in a decoded picture buffer (DPB).

Variations for the IBC prediction mode include, for example, a flippedIBC in which the reference block is flipped horizontally or verticallybefore being used to predict the current block, and line based IBC inwhich each compensation unit inside an M×N coding block is an M×1 or 1×Nline.

FIG. 8 shows an example of an intra block copy (IBC) prediction mode,according to an embodiment of the disclosure. In the example of FIG. 8,a current picture (800) is being reconstructed and includes areconstructed area (801) (gray area) and a to-be-reconstructed area(802) (white area). The blocks in the reconstructed area (801) arealready decoded and the blocks in the to-be-reconstructed area (802) areeither being decoded or to-be-decoded. A current block (804) is in theto-be-reconstructed area (802) and being decoded. The current block(804) can be decoded from a reference block (805) that is in thereconstructed area (801). The decoding of the current block (804) isbased on a block vector (803) that indicates an offset between thecurrent block (804) and the reference block (805).

According to aspects of the disclosure, a reference block (e.g.,reference block (805)) used to derive a block vector (e.g., block vector(803)) for a current block (e.g., current block (804)) is within anallowed reference area of the IBC prediction mode. When the allowedreference area is accessible from a memory with a limited memory space,such as an on-chip memory, the allowed reference area may be constrainedwithin a certain area.

According to some embodiments, an allowed reference area of the IBCprediction mode is constrained to be within a current CTU in which acurrent block resides. In an example, a memory to store referencesamples for the allowed reference area in the IBC prediction mode is 1CTU size (e.g., 128×128 samples). If 1 CTU size (128×128 samples)includes four regions with each region having 64×64 samples, the memorymay store the four regions, in which one region of 64×64 samples may becurrently reconstructed and the other three regions of 64×64 may be usedas reference samples.

According to some embodiments, an allowed reference area of the IBCprediction mode can be extended to some parts of another CTU (e.g., aleft CTU of the current CTU) while keeping the memory size to store theallowed reference area unchanged (e.g., 1 CTU size), so that the allowedreference area may not be constrained to be within the current CTU. Itis noted that the allowed reference area may depend on a position of acurrent block in the current CTU. That is, the allowed reference areamay be updated according to the position of the current block in thecurrent CTU.

FIGS. 9A-9D show examples of allowed reference areas in an updatingprocess of the IBC prediction mode, according to an embodiment of thedisclosure. As described above, the effective allowed reference area canbe extended to some parts of a previous CTU (e.g., left CTU (910)) of acurrent CTU (900).

During the updating process, the stored reference samples from the leftCTU are updated with the reconstructed samples from the current CTU. InFIGS. 9A-9D, gray color regions indicate already reconstructed regions,white color regions indicate to-be-reconstructed regions, and regionswith vertical stripes and text “Curr” indicate current coding/decodingregions where current blocks reside. In addition, in each figure, theleft four regions (911)-(914) belong to the left CTU (910) and the rightfour regions (901)-(904) belong to the current CTU (900).

It is noted that all of four regions (911)-(914) of the left CTU (910)are already reconstructed. Thus, the memory initially stores all ofthese four regions of reference samples from the left CTU (910), andthen a region of reference samples from the left CTU (910) stored in thememory is updated (or replaced) with a same relative region of currentlyreconstructed samples from the current CTU (900).

For example, in FIG. 9A, a current region (901) in the current CTU (900)is under reconstruction, and a co-located region in the left CTU (910)of the current region (901) is an already reconstructed region (911).The co-located region (911) is in a region of the left CTU (910) withthe same relative region as the current block (901) in the current CTU(900). Thus, the memory region that stores reference samples of theco-located region (911) is updated to store the reconstructed samples ofthe current region (901), and an “X” is marked in the co-located region(911) in FIG. 9A to indicate that the reference samples of theco-located region (911) are no longer stored in the memory.

Similarly, in FIG. 9B, a current region (902) in the current CTU (900)is under reconstruction, and a co-located region in the left CTU (910)of the current region (902) is a region (912). The co-located region(912) is in a region of the left CTU (910) with the same relative regionas the current region (902) in the current CTU (900). Thus, the memoryregion that stores reference samples of the co-located region (912) isupdated to store the reconstructed samples of the current region (902),and an “X” is marked in the co-located region (912) in FIG. 9B toindicate that the reference samples of the co-located region (912) areno longer stored in the memory.

In FIG. 9C, a current region (903) in the current CTU (900) is underreconstruction, and a co-located region in the left CTU (910) of thecurrent region (903) is a region (913). The co-located region (913) isin a region of the left CTU (910) with the same relative region as thecurrent region (903) in the current CTU (900). Thus, the memory regionthat stores reference samples of the co-located region (913) is updatedto store the reconstructed samples of the current region (903), and an“X” is marked in the co-located region (913) in FIG. 9C to indicate thatthe reference samples of the co-located region (913) are no longerstored in the memory.

In FIG. 9D, a current region (904) in the current CTU (900) is underreconstruction, and a co-located region in the left CTU (910) of thecurrent region (904) is a region (914). The co-located region (914) isin a region of the left CTU (910) with the same relative region as thecurrent region (904) in the current CTU (900). Thus, the memory regionthat stores reference samples of the co-located region (914) is updatedto store the reconstructed samples of the current region (904), and an“X” is marked in the co-located region (914) in FIG. 9D to indicate thatthe reference samples of the co-located region (914) are no longerstored in the memory.

In FIGS. 9A-9D, it is assumed that the total memory size is equal to 1CTU size (e.g., largest CTU size). According to aspects of thedisclosure, when the CTU size is different (e.g., smaller) from thelargest CTU size, in addition to the reconstructed part of the currentCTU, reference samples from the N−1 left CTUs can also be stored in thememory to be available for reference, where N=Memory size/CTU width/CTUwidth.

For example, if the memory size is 128×128 luma samples, and CTU size is64×64 luma samples, then N=4 and the reference samples in the 3 leftCTUs relative to the current CTU are fully available for IBC prediction.The reference samples in the 4th left CTU relative to the current CTUmay be used but may not need to be considered as a reference area.

According to aspects of the disclosure, when a memory (e.g., referencesample memory) is used for IBC reference sample storage, the memory canbe partitioned into several regions, each of which can have the samesize. The reference sample memory can have the same size as the largestCTU (e.g., 128×128). In an example, for the 128×128 CTU, the referencesample memory can be partitioned into four 64×64 regions, each of whichcontains samples of the corresponding regions in either the current CTUor one region of the left CTU. In another example, for the 64×64 CTU,the reference sample memory can be partitioned into four 64×64 regions,each of which contains samples of the current entire 64×64 CTU orsamples of an entire CTU of the left 64×64 CTUs. In another example, forthe 32×32 CTU, the reference sample memory can be partitioned intosixteen 32×32 regions, each of which contains samples of the currententire 32×32 CTU or samples of an entire CTU of the left 32×32 CTUs.

In some examples, a buffer, referred to as ibcBuffer, with size beingequal to the size of the reference sample memory is used to store thereference samples for IBC prediction. For the 128×128 CTU, the buffersize is 128×128. For the 64×64 CTU, the buffer size is 256×64. For the32×32 CTU, the buffer size is 512×32. When locations in the ibcBufferare not allowed to be used for IBC reference, the sample values at thoselocations in the buffer are marked as “−1” or any value that is not inthe valid range of video samples. The buffer is set to be −1 for allentries at the beginning of a CTU row, and for each current vSize xvSize region, where vSize is the maximum decoding size. In an example,if the CTU size is 64×64 or 128×128, vSize=64; for 32×32 CTU, vSize=32.A reference block inside the buffer can be allowed to be used for IBCprediction only when all sample values in the reference blocks are validvalues.

In an embodiment where the ibcBuffer is used for IBC prediction, at thebeginning of each CTU row, the maximum decoding size vSize is set asmin(ctbSize, 64) and the width of the buffer wIbcBuf is set as(128×128/ctbSize).

For a location (x0, y0) in the ibcBuffer, when x0 is equal to 0 and (y0%ctbSize) is equal to 0, the following applies,

ibcBuffer[x% wIbcBuf][y% ctbSize]=−1,

where x=x0 . . . x0+wIbcBuf−1 and y=y0 . . . y0+ctbSize−1.

At the beginning of each vSize x vSize region, when (x0% vSize) is equalto 0 and (y0% vSize) is equal to 0, the following applies,

ibcBuffer[x% wIbcBuf][y% ctbSize]=−1,

where x=x0 . . . x0+ctbSize−1 and y=y0 . . . y0+ctbSize−1.

After decoding the luma block vector mvL, the luma block vector mvL canbe confined by the following constraints:

((yCb+(mvL[1]>>4))% ctbSize)+cbHeight<ctbSize; and  (1)

ibcBuf[(x+(mvL[0]>>4))% wIbcBuf][(y+(mvL[1]>>4))% ctbSize]!=−1,  (2)

where x=xCb . . . xCb+cbWidth−1 and y=yCb . . . yCb+cbHeight−1.

The first condition is to make sure the reference block cannot besimultaneously from the top of the buffer and the bottom of the buffer,in which case the top corner of the reference block is around the bottompart of the ibcBuffer and the bottom corner of the reference block ismapped to the top part of the ibcBuffer (e.g., vertical wrap-around).

During the compensation stage, the reference samples can be derived fromthe buffer as follows:

predSamples[x][y]=ibcBuffer[(x+mv[0]>>4)% wIbcBuf][(y+mv[1]>>4)%ctbSize],

where x=xCb . . . xCb+Width−1 and y=yCb . . . yCb+Height−1.

After decoding the current coding unit, the reconstructed samples can beput into the buffer ibcBuffer as follows:

ibcBuffer[(xCurr+i)% wIbcBuf][(yCurr+j)%ctbSize]=recSamples[xCurr+i][yCurr+j],

where i=0 . . . nCurrSw−1 and j=0 . . . nCurrSh−1.

According to aspects of the disclosure, reference samples in a picture,when copied into the reference sample memory, can be in part refreshedby some updated samples from newly coded CUs. When a block vector pointsto a specific location inside the reference sample memory, it ispossible that different parts of the reference block may come fromdifferent regions of the reference sample memory. For example, thebottom right part of the reference block in the reference sample memorymay not come from the same reference region which the top left part ofthe reference block in the reference sample memory belongs to.

FIGS. 10A and 10B show examples in which samples of the reference blockare from different regions of the reference sample memory. In FIGS. 10Aand 10B, both sizes of a current CTU (1010) and a left CTU (1020) are128×128 luma samples. The grey areas are already reconstructed parts ofthe current picture. The white areas are not yet reconstructed part ofthe current picture. The size of the reference sample memory is also128×128 and partitioned into four 64×64 regions (1031)-(1034). Theregions with “X” are not allowed to be used as reference areas due tomemory constraints.

In FIG. 10A, a current block (1001) is at the bottom-right corner of thecurrent CTU (1010). A reference block (1002) (i.e., dashed block) of thecurrent block (1001) has the same size as the current block (1001). Itcan be seen that different parts of the reference block (1002) are fromdifferent memory regions of the reference sample memory. For example,the top-left part of the reference block (1002) is from the memoryregion (1031) while the bottom-right part of the reference block (1002)is from the memory region (1034).

In FIG. 10B, a current block (1003) is at the top-right corner of thecurrent CTU (1010). A reference block (1004) (i.e., dashed block) of thecurrent block (1003) has the same size as the current block (1003). Itcan also be seen that different parts of the reference block (1004) arefrom different memory regions of the reference sample memory. Forexample, the top-left part of the reference block (1004) is from thememory region (1032) while the top-right part of the reference block(1004) is from the memory region (1034). In addition, the bottom-rightpart of the reference block (1004) actually contains samples (1005) fromthe left CTU (1020) since the bottom-right 64×64 region of the currentCTU (1010) is not yet decoded.

Accordingly, in both FIGS. 10A and 10B, 4 different regions of thereference sample memory are accessed in order to generate the referenceblocks (1002) and (1004) for the IBC prediction. It is desirable if suchmemory access can be simplified and a number of memory accesses can bereduced.

III. Proposed Constraints on Reference Sample Locations for IBC

Aspects of the disclosure provide methods of constraining referencesample locations in a reference sample memory for IBC prediction. Thereference sample memory can include different memory regions for thepurpose of storing reference samples from different parts of the pictureor for adapting into certain processing capacities. Examples of suchmemory regions in a 128—x128 memory, including either 64×64, 32×32, orother values, are described above.

According to aspects of the disclosure, a location of a reference blockin the reference sample memory can be confined in a way such that anumber of different regions in the reference sample memory that containsamples of the reference block can be limited to a certain number.Without such a constraint, the maximum number of regions in thereference sample memory that may contain samples of the reference blockcan be the total number of the memory regions in the reference samplememory, such as 4, as shown in both FIGS. 10A and 10B. When constrainingthe reference block to be within a certain number of memory regions inthe reference sample memory, the need to access different memory regionscan reduced.

FIG. 11 shows examples where the samples of the reference block areconstrained to be within a certain number of memory regions in thereference sample memory. In FIG. 11, the reference sample memory has asize of 128×128 luma samples and is partitioned into four 64×64 regions(1111)-(1114).

In some embodiments, the entire reference block can be located in a samememory region. Accordingly, the number of memory regions in the bufferrelated to the generation of the reference block can be only 1. Forexample, for a current block (1101) located at the bottom-right cornerof a current CTU (1110), a reference block can be a dashed block (1102),which is entirely located inside the memory region (1112).

In one embodiment, the CTU size is the same as the size of the referencesample memory (e.g., 128×128), and the reference sample memory isorganized (or partitioned) into multiple regions (e.g., multiple 64×64regions). The entire reference block can be constrained to be locatedinside a same 64×64 region predefined in the reference sample memory.

In one embodiment, the CTU size is smaller than the size of thereference sample memory. For example, the size of the reference samplememory is 128×128 and the CTU size is 64×64. The entire reference blockcan be constrained to be located inside a same 64×64 region predefinedin the reference sample memory.

In one embodiment, the CTU size is smaller than the size of thereference sample memory. For example, the size of the reference samplememory is 128×128 and the CTU size is 32×32. The entire reference blockcan be constrained to be located inside a same 32×32 region predefinedin the reference sample memory.

In the above embodiments in which the entire reference block is locatedin the same memory region, constraints may be imposed in both x (i.e.,horizontal) and y (i.e., vertical) directions of the luma block vectormvL. For example, the luma block vector mvL can be constrained asfollows:

((xCb+(mvL[0]>>4))% vSize)+cbWidth<vSize;  (1)

((yCb+(mvL[1]>>4))% vSize)+cbHeight<vSize; and  (2)

ibcBuf[(x+(mvL[0]>>4))% wIbcBuf][(y+(mvL[1]>>4))% ctbSize]!=−1,  (3)

where x=xCb . . . xCb+cbWidth−1 and y=yCb . . . yCb+cbHeight−1.

The first two conditions specify that the top-left corner of thereference block and the bottom-right corner of the reference block canbe inside the same region with a size of vSize x vSize. Accordingly, theentire reference block is expected to be inside the same memory region.

In some embodiments, the number of memory regions in the buffer relatedto the generation of the reference block can be limited to be at most 2.

In one embodiment, constraints may be imposed only in the y direction ofthe luma block vector mvL. For example, the luma block vector mvL can beconstrained as follows:

((yCb+(mvL[1]>>4))% vSize)+cbHeight<vSize; and  (1)

ibcBuf[(x+(mvL[0]>>4))% wIbcBuf][(y+(mvL[1]>>4))% ctbSize]!=−1,  (2)

where x=xCb . . . xCb+cbWidth−1 and y=yCb . . . yCb+cbHeight−1.Accordingly, for each x location in the reference block, both the topsamples and bottom samples of the reference block can be located in asame memory region (e.g., an entire column of the samples of thereference block is contained in the same memory region). For example,for the current block (1101), the reference block can be a dashed block(1103), of which a left part is inside the memory region (1111) and aright part is inside the memory region (1113).

In one embodiment, constraints may be imposed only in the x direction ofthe luma block vector mvL. For example, the luma block vector mvL can beconstrained as follows:

((xCb+(mvL[0]>>4))% vSize)+cbWidth<vSize; and  (1)

ibcBuf[(x+(mvL[0]>>4))% wIbcBuf][(y+(mvL[1]>>4))% ctbSize]!=−1,  (2)

where x=xCb . . . xCb+cbWidth−1 and y=yCb . . . yCb+cbHeight−1.Accordingly, for each y location in the reference block, both theleft-most samples and right-most samples of the reference block can belocated in a same memory region (e.g., an entire row of the samples ofthe reference block is contained in the same memory region). Forexample, for the current block (1101), the reference block can be adashed block (1104), of which a top part is inside the memory region(1113) and a bottom part is inside the memory region (1114). It is notedthat the vertical wrap-around case can be allowed in this embodiment.For example, the reference block can be a dashed block (1105), of whicha top part is inside the memory region (1111) and a bottom part (1106)is inside the memory region (1112).

In one embodiment, constraints may be imposed in both x and y directionsof the luma block vector mvL. For example, the luma block vector mvL canbe constrained as follows:

((xCb+(mvL[0]>>4))% vSize)+cbWidth<vSize;  (1)

((yCb+(mvL[1]>>4))% ctbSize)+cbHeight<ctbSize; and  (2)

ibcBuf[(x+(mvL[0]>>4))% wIbcBuf][(y+(mvL[1]>>4))% ctbSize]!=−1,  (3)

where x=xCb . . . xCb+cbWidth−1 and y=yCb . . . yCb+cbHeight−1.Accordingly, for each y location in the reference block, both theleft-most samples and right-most samples of the reference block can belocated in a same memory region. In addition, for each x location in thereference block, the top samples of the reference block are always abovethe bottom samples of the reference block along y direction. That is,the vertical wrap-around case is not allowed in this embodiment (e.g., atop row of the samples of the reference block is above a bottom row ofthe samples of the reference block along a vertical direction).Therefore, for the current block (1101), the reference block can be thedashed block (1104) but cannot be the dashed block (1105).

In the above embodiments, the modulo operation “x % y” is used to obtainthe address inside the reference sample memory and may be replaced by a“bit wise AND” operation, such as “x&(y−1)”. For example, the expression((xCb+(mvL[0]>>4))% vSize) can be replaced by the expression((xCb+(mvL[0]>>4))&(vSize−1)).

IV. Flowchart

FIG. 12 shows a flow chart outlining an exemplary process (1200)according to an embodiment of the disclosure. In various embodiments,the process (1200) is executed by processing circuitry, such as theprocessing circuitry in the terminal devices (210), (220), (230) and(240), the processing circuitry that performs functions of the videoencoder (303), the processing circuitry that performs functions of thevideo decoder (310), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the intra prediction module (452), the processing circuitrythat performs functions of the video encoder (503), the processingcircuitry that performs functions of the predictor (535), the processingcircuitry that performs functions of the intra encoder (622), theprocessing circuitry that performs functions of the intra decoder (772),and the like. In some embodiments, the process (1200) is implemented insoftware instructions, thus when the processing circuitry executes thesoftware instructions, the processing circuitry performs the process(1200).

The process (1200) may generally start at step (S1210), where theprocess (1200) decodes prediction information of a current block of aCTU in a coded bitstream. The prediction information indicates that thecurrent block is coded in IBC mode. Then the process (1200) proceeds tostep (S1220).

At step (S1220), the process (1200) determines a reference block for thecurrent block. A number of memory regions that contain samples of thereference block is less than a total number of memory regions for theCTU. Then the process (1200) proceeds to step (S1230).

At step (S1230), the process (1200) reconstructs the current block basedon the reference block. After reconstructing the current block, theprocess (1200) terminates.

In an embodiment, the entire reference block is contained in one memoryregion of the memory regions for the CTU.

In an embodiment, a size of the one memory region is equal to a sizethreshold based on a size of the CTU being greater than or equal to thesize threshold.

In an embodiment, a size of the one memory region is equal to a size ofthe CTU based on the size of the CTU being less than a size threshold.

In an embodiment, an entire column of the samples of the reference blockis contained in one of the memory regions for the CTU.

In an embodiment, an entire row of the samples of the reference block iscontained in one of the memory regions for the CTU.

In an embodiment, a top row of the samples of the reference block isabove a bottom row of the samples of the reference block along avertical direction.

V. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 13 shows a computersystem (1300) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 13 for computer system (1300) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1300).

Computer system (1300) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1301), mouse (1302), trackpad (1303), touchscreen (1310), data-glove (not shown), joystick (1305), microphone(1306), scanner (1307), camera (1308).

Computer system (1300) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1310), data-glove (not shown), or joystick (1305), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1309), headphones(not depicted)), visual output devices (such as screens (1310) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability-some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1300) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1320) with CD/DVD or the like media (1321), thumb-drive (1322),removable hard drive or solid state drive (1323), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1300) can also include an interface (1354) to one ormore communication networks (1355). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CANBus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general purpose data ports or peripheral buses (1349) (such as,for example USB ports of the computer system (1300)); others arecommonly integrated into the core of the computer system (1300) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (1300) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1340) of thecomputer system (1300).

The core (1340) can include one or more Central Processing Units (CPU)(1341), Graphics Processing Units (GPU) (1342), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1343), hardware accelerators for certain tasks (1344), graphics adapter(1350), and so forth. These devices, along with Read-only memory (ROM)(1345), Random-access memory (1346), internal mass storage such asinternal non-user accessible hard drives, SSDs, and the like (1347), maybe connected through a system bus (1348). In some computer systems, thesystem bus (1348) can be accessible in the form of one or more physicalplugs to enable extensions by additional CPUs, GPU, and the like. Theperipheral devices can be attached either directly to the core's systembus (1348), or through a peripheral bus (1349). In an example, a display(1310) can be connected to the graphics adapter (1350). Architecturesfor a peripheral bus include PCI, USB, and the like.

CPUs (1341), GPUs (1342), FPGAs (1343), and accelerators (1344) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1345) or RAM (1346). Transitional data can be also be stored in RAM(1346), whereas permanent data can be stored for example, in theinternal mass storage (1347). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1341), GPU (1342), massstorage (1347), ROM (1345), RAM (1346), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1300), and specifically the core (1340) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1340) that are of non-transitorynature, such as core-internal mass storage (1347) or ROM (1345). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1340). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1340) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1346) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1344)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

APPENDIX A: ACRONYMS

-   AMVP: Advanced Motion Vector Prediction-   ASIC: Application-Specific Integrated Circuit-   ATMVP: Alternative/Advanced Temporal Motion Vector Prediction-   BMS: Benchmark Set-   BV: Block Vector-   CANBus: Controller Area Network Bus-   CB: Coding Block-   CD: Compact Disc-   CPR: Current Picture Referencing-   CPUs: Central Processing Units-   CRT: Cathode Ray Tube-   CTBs: Coding Tree Blocks-   CTUs: Coding Tree Units-   CU: Coding Unit-   DPB: Decoder Picture Buffer-   DVD: Digital Video Disc-   FPGA: Field Programmable Gate Areas-   GOPs: Groups of Pictures-   GPUs: Graphics Processing Units-   GSM: Global System for Mobile communications-   HEVC: High Efficiency Video Coding-   HRD: Hypothetical Reference Decoder-   IBC: Intra Block Copy-   IC: Integrated Circuit-   JEM: Joint Exploration Model-   LAN: Local Area Network-   LCD: Liquid-Crystal Display-   LTE: Long-Term Evolution-   MV: Motion Vector-   MVP: Motion Vector Prediction-   OLED: Organic Light-Emitting Diode-   PBs: Prediction Blocks-   PCI: Peripheral Component Interconnect-   PLD: Programmable Logic Device-   PUs: Prediction Units-   RAM: Random Access Memory-   ROM: Read-Only Memory-   SCC: Screen Content Coding-   SEI: Supplementary Enhancement Information-   SNR: Signal Noise Ratio-   SSD: Solid-state Drive-   TUs: Transform Units-   USB: Universal Serial Bus-   VUI: Video Usability Information-   VVC: Versatile Video Coding

What is claimed is:
 1. A method for video coding in an encoder,comprising: determining a block vector of a current block of a codingtree unit (CTU) that is coded in intra block copy (IBC) mode, the blockvector indicating a reference block in a search region for the currentblock, reference samples used to reconstruct the current block in theIBC mode being contained in a reference sample memory including aplurality of memory regions; and coding the current block based on thereference block, wherein a subset of the plurality of memory regions ofthe reference sample memory is used as the search region, and the blockvector of the current block is constrained such that the reference blockis contained in (i) one of the subset of the plurality of memory regionsor (ii) two adjacent memory regions in the subset of the plurality ofmemory regions.
 2. The method of claim 1, wherein a size of each of theplurality of memory regions of the reference sample memory is based on acomparison between a size of the CTU and a size threshold.
 3. The methodof claim 2, wherein the size of each of the plurality of memory regionsof the reference sample memory is equal to the size threshold based onthe size of the CTU being greater than or equal to the size threshold.4. The method of claim 2, wherein the size of each of the plurality ofmemory regions of the reference sample memory is equal to the size ofthe CTU based on the size of the CTU being less than the size threshold.5. The method of claim 1, wherein a first constraint is applied to avertical component of the block vector of the current block such that aleft part and a right part of the reference block are respectivelycontained in the two adjacent memory regions in the subset of theplurality of memory regions.
 6. The method of claim 1, wherein a secondconstraint is applied to a horizontal component of the block vector ofthe current block such that a top part and a bottom part of thereference block are respectively contained in the two adjacent memoryregions in the subset of the plurality of memory regions.
 7. The methodof claim 1, wherein a first constraint is applied to a verticalcomponent of the block vector of the current block and a secondconstraint is applied to a horizontal component of the block vector ofthe current block such that the entire reference block is contained inthe one of the subset of the plurality of memory regions.
 8. Anapparatus, comprising processing circuitry configured to: determining ablock vector of a current block of a coding tree unit (CTU) that iscoded in intra block copy (IBC) mode, the block vector indicating areference block in a search region for the current block, referencesamples used to reconstruct the current block in the IBC mode beingcontained in a reference sample memory including a plurality of memoryregions; and code the current block based on the reference block,wherein a subset of the plurality of memory regions of the referencesample memory is used as the search region, and the block vector of thecurrent block is constrained such that the reference block is containedin (i) one of the subset of the plurality of memory regions or (ii) twoadjacent memory regions in the subset of the plurality of memoryregions.
 9. The apparatus of claim 8, wherein a size of each of theplurality of memory regions of the reference sample memory is based on acomparison between a size of the CTU and a size threshold.
 10. Theapparatus of claim 9, wherein the size of each of the plurality ofmemory regions of the reference sample memory is equal to the sizethreshold based on the size of the CTU being greater than or equal tothe size threshold.
 11. The apparatus of claim 9, wherein the size ofeach of the plurality of memory regions of the reference sample memoryis equal to the size of the CTU based on the size of the CTU being lessthan the size threshold.
 12. The apparatus of claim 8, wherein a firstconstraint is applied to a vertical component of the block vector of thecurrent block such that a left part and a right part of the referenceblock are respectively contained in the two adjacent memory regions inthe subset of the plurality of memory regions.
 13. The apparatus ofclaim 8, wherein a second constraint is applied to a horizontalcomponent of the block vector of the current block such that a top partand a bottom part of the reference block are respectively contained inthe two adjacent memory regions in the subset of the plurality of memoryregions.
 14. The apparatus of claim 8, wherein a first constraint isapplied to a vertical component of the block vector of the current blockand a second constraint is applied to a horizontal component of theblock vector of the current block such that the entire reference blockis contained in the one of the subset of the plurality of memoryregions.
 15. A non-transitory computer-readable storage medium storing aprogram executable by at least one processor to perform: determining ablock vector of a current block of a coding tree unit (CTU) that iscoded in intra block copy (IBC) mode, the block vector indicating areference block in a search region for the current block, referencesamples used to reconstruct the current block in the IBC mode beingcontained in a reference sample memory including a plurality of memoryregions; and coding the current block based on the reference block,wherein a subset of the plurality of memory regions of the referencesample memory is used as the search region, and the block vector of thecurrent block is constrained such that the reference block is containedin (i) one of the subset of the plurality of memory regions or (ii) twoadjacent memory regions in the subset of the plurality of memoryregions.
 16. The non-transitory computer-readable storage medium ofclaim 15, wherein a size of each of the plurality of memory regions ofthe reference sample memory is based on a comparison between a size ofthe CTU and a size threshold.
 17. The non-transitory computer-readablestorage medium of claim 16, wherein the size of each of the plurality ofmemory regions of the reference sample memory is equal to the sizethreshold based on the size of the CTU being greater than or equal tothe size threshold.
 18. The non-transitory computer-readable storagemedium of claim 16, wherein the size of each of the plurality of memoryregions of the reference sample memory is equal to the size of the CTUbased on the size of the CTU being less than the size threshold.
 19. Thenon-transitory computer-readable storage medium of claim 15, wherein afirst constraint is applied to a vertical component of the block vectorof the current block such that a left part and a right part of thereference block are respectively contained in the two adjacent memoryregions in the subset of the plurality of memory regions.
 20. Thenon-transitory computer-readable storage medium of claim 15, wherein asecond constraint is applied to a horizontal component of the blockvector of the current block such that a top part and a bottom part ofthe reference block are respectively contained in the two adjacentmemory regions in the subset of the plurality of memory regions.